The invention relates to a vacuum switch provided with two contacts of electrically conductive material which can be moved towards and away from each other, mounted on the ends of a fixed or movable contact rod respectively of electrically conductive material, with a laminated horseshoe-shaped ferromagnetic element being fitted around each contact rod, as a result of which because of its position a magnetic circuit is formed, around the contact rod, which consists of a section of low magnetic resistance and a section of high magnetic resistance, the circular base of the U-shaped inner cavity of the horseshoe-shaped elements being adjacent to the associated contact rod and the elements being offset through 180.degree. with respect to each other, so that the internal magnetic fields generated in the horseshoe-shaped elements when current passes through the switch, to the extent that the section with high magnetic resistance is approached, are mainly oriented axially between the two horseshoe-shaped elements.
A vacuum switch of this type is disclosed in Dutch Patent No. 168,361.
In this, in a very simple way, a powerful axial magnetic field is generated by means of the ferromagnetic horseshoe-shaped elements, with the result that the arc voltage is limited and the circuit-breaking characteristics of the vacuum switch are improved.
Although the ferromagnetic horseshoe-shaped elements according to the above-rated Dutch Patent show a marked improvement in relation to the arc voltage and consequently the switching performance of the vacuum switch, the latter still has a number of drawbacks.
Specifically, if there is a requirement to increase the arc voltage and consequently the circuit-breaking breaking capacity still further by intensifying the axial field, this would mean that the volume of the ferromagnetic horseshoe-shaped elements would have to increase. However, in view of the position of the ferromagnetic horseshoe-shaped elements within the switch, such an increase would at the same time imply that the dimensions of the switch would increase. However, this is incompatible with the general aim of keeping the dimensions of the vacuum switches as limited as possible. In addition, the mass of the movable contact will then likewise increase, which would place higher demands on the drive mechanism and lead to an increased tendency for the contacts to rumble on closing.